ILLNESS AND CURE:Medical Correspondent Dr Muiris Houstonanswers questions many are asking about the disease
Is the virus now affecting people in different continents a swine flu or human influenza?
The H1N1 flu virus has its origins in pigs in Mexico. However, detailed analysis of the organism has revealed genetic material from pigs, birds and humans. So it seems likely the new virus emerged from a mixing together of pre-existing influenza bugs – in genetic reassortment – to produce a virus easily transmitted from pig to human and between humans.
It will probably be referred to as swine flu because that is its species of origin, although it may subsequently be labelled Mexican flu in line with a tradition producing Spanish and Hong Kong influenza.
Why have some of those infected in Mexico died while the illness appears to be milder in people in the US, Canada and New Zealand?
The reason for this remains unclear. It could be the infection was spreading in Mexico for longer than thought, so we are seeing deaths at a later stage in the illness. It could be that anti-viral and other medical care was given late in their illness to those who have died and that prompt treatment in more developed countries means the illness is less severe.
It is possible other diseases that reduce the immune system’s effectiveness were present in those who have died. And it may be the virus is attenuated after transferring from pig to human so those who contract the disease by means of human-to-human transmission experience milder illness.
What must happen for the World Health Organisation (WHO) to further increase the threat level from four to five?
There must be evidence of human-to-human transmission of the H1N1 influenza A virus in at least two countries. Therefore it is possible to reach threat level five with no cases in Ireland. However, the pandemic influenza expert group here has devised a four-level alert system to complement the WHO system. If the new virus is isolated from a patient in Ireland, we move to alert level two, while an Irish outbreak of H1N1 flu triggers alert level three.
How do anti-viral drugs work?
They attack a key protein on the surface of the virus. The protein is called neuraminidase and it enables the replicating influenza virus to break away from the cell it initially invaded and to spread throughout the body.
Neuraminidase inhibitors such as oseltamivir (Tamiflu) and zanamivir (Relenza) prevent newly formed influenza particles from escaping infected cells, thereby interrupting the spread of infection within the body. To be effective, the drug must be started within 48 hours of the onset of flu symptoms. Tamiflu is suitable for adults and children aged one and over. Anti-virals may also be used to prevent infection.